Formatting cells on your worksheet can make the right information easy to see at a glance, but formatting cells that aren't being used (especially entire rows and columns) can cause your workbook's file size to grow quickly. This can slow down not just Excel, but the overall performance of your computer when you have an excessively formatted worksheet open. Excessive formatting can also cause printing problems in Excel.
Use the Clean Excess Cell Formatting command, available on Excel's Inquire tab in Microsoft Office 365 and Office Professional Plus 2013. If you don't see the Inquire tab in Excel, do the following to enable the Inquire add-in:
Click File > Options > Add-Ins.
Make sure COM Add-ins is selected in the Manage box, and click Go.
In the COM Add-Ins box, check Inquire, and then click OK.
The Inquire tab should now be visible in the ribbon.
Important: You may want to make a backup copy of your file before cleaning the excess cell formatting, because there are certain cases where this process may make your file increase in size, and there is no way to undo the change.
To remove the excess formatting in the current worksheet, do the following:
On the Inquire tab, click Clean Excess Cell Formatting.
Choose whether to clean only the active worksheet or all worksheets. After excess formatting has been cleared, click Yes to save changes to the sheets or No to cancel.
How cleaning affects conditional formatting
Cleaning excess formatting works by removing cells from the worksheet that are beyond the last cell that isn't blank For example, if you apply conditional formatting to an entire row, but your data goes out only to column V, the conditional formatting may be removed from columns beyond column V.
To learn more about how to fix other problems caused by excessive formatting , see the Microsoft Support article How to reset the last cell in Excel.